Optical measuring devices are used in monitoring, controlling and managing processes. An example of an optical measuring device is a refractometer, which measures the refractive index of a process medium by means of the total reflection created at the interface between an optical window and the process medium.
The process medium measured by an optical measuring device may be hot, pressurized, aggressive or otherwise hazardous. The failure of operation, e.g. a leakage into the optical measuring device from the process, is often detected by a humidity sensor and/or the electronics inside the optical measuring device. This prevents injuries resulting from a fitting or a connection failure and protects the measuring device and the user.
If the process medium is food products, e.g. dairy, liquid food, liquid sugar or beverage, a leakage into the optical measuring device poses a contamination risk. The growth of spoilage and pathogenic bacteria starts in the leaked process medium inside the optical measuring device. Then, if the pressure on the process side drops the contaminated leaked process medium is conveyed to the process medium.
The problem with the arrangement described above is that upon a failure in the fittings or connections between the process medium and the optical measuring device the user does not notice the failure and the pressure difference between the process medium and the interior of the optical measuring device pushes the leaked process medium back to the process side. The failure may also remain undetected by a humidity sensor and/or the electronics inside the optical measuring device if they are not turned on for one reason or another.